Yep. I'm no expert either and haven't experimented much like 318WR does but you need some compression. The Teens weren't high compression engines and if you bolt on a set of heads with a big ol' open chamber designed for 4" bores and use a thick ol' head gasket and throw in a big ol' cam with lots of duration (that bleeds off compression) you might have to spin it to 5 g's or better to make your big port heads to flow. Whew, that was one long sentence!